1. Field of the Invention
The present invention relates to a wavelength conversion element for car use, which utilizes emitted light wavelengths from a light emitting diode (hereinafter referred as “LED”) made of compound semiconductors, particularly for a headlight or the like.
2. Brief Description of the Related Art
An invention disclosed in Japanese laid open patent No.7-99345 is a well known example of wavelength conversion elements.
As illustrated in a schematic cross-sectional view in FIG. 12, an emitting chip 1 of an LED constituted by compound semiconductors is mounted on a cup 2 of a lead frame 3. The LED is sealed by a combination of two resins, the first one is a resin 4 which fills the inside of the cup 2 and the second one is a resin 5 which surrounds the resin 4. A fluorescent material which converts emitted wavelengths from chip 1 into other wavelengths or a wavelength conversion material 6 such as a filter material which absorbs a part of emitted wavelengths is included in the first resin 4, so that luminance and light converging efficiency of the LED are enhanced as being reflected the converted wavelengths by the inner surface of the cup 2.
If the wavelength conversion element for car use by the present invention is employed as a light source of a light assembly of a car, the LED having a high luminous emittance (Im/mm2), which determines a required size of an optical portion of the lamp, is desirable. In other words, it is necessary to concentrate luminous flux from the LED on an area as small as possible. However, in a conventional white LED, since excitation light irradiated from the side surface of the chip, an area where there is a fluorescent material corresponds to a light emitting part, namely, the same area as a reflective horn corresponds to the light emitting plane. Consequently, the light emitting part of the LED is large compared with a projected chip area on a plane perpendicular to an optical axis of the LED. In other words the luminous emittance of the LED is lowered to an extent incapable of being employed as the light source of the lamp assembly for car use.
In the lamp assembly for car use, a light distribution pattern stipulated by the standard is obtained by using reflectors and lenses in front of an emitting plane of the lamp assembly so as to project the emitting plane on an appropriate position.
In the presently available lamp assemblies, which employ halogen bulbs and discharge lamps, the light distribution pattern is controlled by a combination of two optical systems, a reflector and a projection lens as shown in FIG. 13. FIG. 14 shows a schematic light distribution pattern (for keep to left countries) of a passing-by lamp beam, which is required to show a sharp contrast (hereinafter referred as “cut-off”). Namely, light does not reach to an upper area than an approximately horizontal line so that light from a headlight of a car does not dazzle a driver of a passing-by car. In the example illustrated in FIG. 13, the cut-off is realized by inserting a shield plate between a light source and the projection lens.
However, the following drawbacks are accompanied, when the optical system illustrated in FIG. 13 is employed.
1) The number of required parts is increased because of the complicated optical system.
2) Since a deep space is required for the lamp assembly, it is hard to modify the lamp assembly into a compact one.
3) When the LED is employed as a light source with less luminous than a conventional light source (a halogen bulb or HID), it is hard to obtain a required maximum luminosity for the headlight of the car, since an enlarged light source image is projected by a reflector.
4) Luminosity of the lamp assembly is lost through reflection by the reflector, refraction by the lens and shielding by the shield plate.
When the conventional white LED is employed and emitted light is controlled by a reflector only so as to attain a compact lamp assembly, portions a little bit lower than the horizontal line, have maximum luminance as illustrated in FIG. 16, because a center portion of the LED chip has maximum luminosity as illustrated in FIG. 15. Consequently, the required sharp cut-off can not be realized by the conventional white LED.
Recent technical innovations make a GaN type blue LED available by utilizing conductive substrates such as SiC, GaN, Si and the like. When the conductive substrate is applied to the blue LED for the lamp assembly for car use, one surface of the substrate is connected to a cavity of a base by a conductive adhesive and other surface is electrically connected to a lead frame via a wire made of Au or the like, which extends from an electrode arranged in the center of the other surface. Since the above-mentioned extending wire made of Au or the like is projected ahead together with a light emitting surface of the light source of the light assembly for car use, a good light distributing pattern can not be obtained.